Focused high energy beams, including electron beams (also referred to as “e-beams”) and laser beams have been used to melt layers of metallic powder, resulting in the generation of complex geometries. The quality and consistency of a high energy beam is one of the most important factors in determining the final quality of components manufactured using high energy beam melting processes. The generation and control of a high energy beam is a rather complex process. Two current methods used for assessing the quality of an e-beam for use with an electron beam melting (EBM) process are the enhanced modified Faraday cup (EMFC) electron beam welding diagnostic and the beam verification processes.
Referring to FIG. 1, the EMFC system receives a high energy beam through thin slits on the top of a tungsten disc to effectively measure the beam's current, size, shape and peak power distribution. This system has generated a significant amount of informative data regarding beam parameters, including beam quality and previously unquantifiable beam interference factors. This data has led to a deeper understanding into the EBM process and specifically how a high energy beam interacts with the powder bed to form a consistent melt pool. However, a major limitation with the EMFC system is that, due to the requirement for a beam undergoing testing to enter the tungsten disc at a specific angle, the EMFC is only able to analyze the beam in the center of a build area. This limitation leads to an assumption that the measured beam characteristics are accurately replicated across an entire build area over which a beam will travel during manufacturing of a component.
Referring now to FIG. 2, in the beam verification process, a beam is scanned across a stainless steel plate at relatively low beam energies, forming a number of predefined patterns. This process allows for limited beam characterization across an entire build area but is not sensitive to small changes in beam quality that may produce notable effects during an EBM process. This process merely serves as a verification that beam intensity and focus set points are in approximately the correct region in selected areas of the plate. However, the quantity of data generated by this process is insufficient to be used in the manufacture of reliably and reproducibly high quality components.
The calibration of the beam focusing system is an important step that in essence dictates the dimensional accuracy and mechanical properties of a manufactured component. Beam calibration is a manually intensive process that is intended to ensure that the beam demonstrates the smallest spot size, most circular beam and highest intensity at any specified point across the build area. There is no constraint that the beam size, circularity, and intensity at each position are the same. This could mean that although the beam is as intense as possible at each calibration location, there may be variation across the bed, and just as importantly between machines. A further weakness of the beam calibration procedures is their dependence on operator skill leading to significant potential for error and lack of repeatability between successive beam calibrations.
Therefore, there is a need to improve the high energy beam diagnostic process to provide high resolution beam information across entire build areas under representative processing conditions.